The present invention relates in general to a conductive center plate assembly liner for a railroad car, and more particularly to a conductive center plate assembly liner for placement between a car body center plate and a truck bolster bowl in a railroad car, wherein the liner includes a wear resistant load-bearing portion and a plurality of compressible conductive resilient members which provide electrical conductivity between the car body center plate and truck bolster bowl of the center plate assembly.
Conventional freight railroad cars are generally constructed with a body having an underframe including a pair of spaced-apart center plates. The center plates rest on and are rotatably or swivelly received by a pair of spaced-apart trucks. The trucks rollingly support the car along conventional railroad tracks. Each car body is swivelly or rotatably received by a truck bolster by a conventional center plate assembly that includes a car body center plate attached to the underframe, a truck bolster bowl attached to the truck, and a liner, bearing or wear element positioned between the center plate and the bowl. A conventional kingpin extends through the car body center plate and the truck bolster bowl. The liners have generally been horizontal or disk-shaped, cup-shaped or bowl-shaped.
Such liners must provide electrical continuity or conductivity between the car body center plate and the truck bolster bowl. This electrical continuity or conductivity provides a ground for the railroad car body which eliminates or reduces the buildup of static electricity on the car body. The electric continuity or conductivity also provides the ability to obtain signals through the railroad tracks or rails.
Manganese steel liners were used as wear elements in center plate assemblies for many years in the railroad industry. The steel liners provided electrical continuity between the car body center plate and the truck bolster bowl. However, the steel liners did not significantly reduce wear to the center plate or the bowl and required periodic lubrication.
To solve this problem, certain types of plastic center plate assembly wear liners have been used between the car body center plate and the truck bolster bowl to reduce wear on these parts by eliminating the metal-to-metal contact incurred with the steel liners. These plastic liners are self-lubricating and thus reduce the wear to these parts. Plastic liners, however, do not provide the necessary electrical continuity between the car body center plate and the truck bolster bowl.
To solve this problem, solid brass, copper or other metal electrically conductive studs or pins have been placed in these plastic liners to provide metal-to-metal contact between the center plate and bowl to create electrical continuity. These studs or pins engage both center plate and bowl to provide the electrical continuity. However, these metal studs or pins substantially increase the friction between the center plate and bowl. Moreover, the heads of these metal studs or pins tend to break or wear off and then become less effective and possibly not effective at all in providing electrical continuity between the car body center plate and the truck bolster bowl.
To solve this problem, certain plastic liners have been made with inner conductive rings as disclosed in U.S. Pat. Nos. 5,908,001, 6,136,240 and 6,041,714. However, a potential problem with such liners is a lack of conductivity between the car body center plate and the truck bolster bowl due to uneven seating of the center plate in the bowl, the build-up of grease and dirt and irregular surfaces of the center plate and the bowl. Additionally, since these liners have been commercially made from an ultra-high-weight polyethylene (xe2x80x9cUHMWPExe2x80x9d), they are potentially subject to cold flow under the weight of the freight car supported by the car body center plates. There is currently no known solution to these problems.
Accordingly, while there has been a steady progression of improvements of the liners for center plate assemblies of railroad cars, there is still a need for an improved railroad car center plate assembly liner which ensures better conductivity than known liners and is more resistant to cold flow than known liners.
The present invention overcomes the above problems by providing a railroad car center plate assembly liner which ensures better conductivity than known liners and is more resistant to cold flow than known liners. The liner of one embodiment of the present invention includes a self-lubricating load-bearing portion that withstands abrasion and substantially resists cold flow. The liner includes at least one and preferably a plurality of spaced-apart symmetrically arranged compressible conductive resilient members positioned in the load-bearing portion. Each of the conductive resilient members slightly transversely extend above and below the planes of the top and bottom surfaces, respectively, of the load-bearing portion of the liner to facilitate the electric conductivity between the truck bolster bowl and the car body center plate. As described in more detail below, the conductive members are made from a resilient material which enables them to continue to provide electric continuity even when they are compressed, deformed or crushed under the weight of the railroad car.
In one embodiment of the present invention, the body of the liner including the load-bearing portion of the liner is made of a urethane, and in one preferred embodiment is made of a glass-filled urethane. In this embodiment, the glass reinforces the load-bearing portion. The glass may be in granules, fibers or other suitable forms. The word xe2x80x9cparticlexe2x80x9d used herein is intended to include granules and/or fibers of any suitable type and such other suitable forms. The glass-filled urethane load-bearing portion substantially resists cold flow from the weight of the car. The body of the liner is preferably injection molded.
In one preferred embodiment of the present invention, the conductive resilient members of the liner are made of a urethane to resist cold flow and to be sufficiently compressible or resilient. The conductive members include conductive particles such as carbon black particles which make these members conductive. The urethane conductive members are preferably unfilled except with the conductive particles because urethane has a greater memory characteristic which provides sufficient resiliency to the members and enables them to function in a spring-like manner to maintain contact with the center plate and bowl and also to compensate for irregular surfaces of the center plate and bowl. In other words, the conductive members have a rubber-like characteristic and are resilient enough to push upwardly and downwardly in a similar fashion to a coil spring. This is substantially different than the previous known metal studs which tend to break because they had no relative resiliency. The conductive members are preferably preformed injection molded members. It should be appreciated that the conductive members could alternatively be partially filled with strengthening material such as glass particles to add a desired amount of strength to the members; however, such additional strength would reduce the memory effect of the compressible conductive members.
It is therefore an advantage of the present invention to provide a center plate assembly liner for placement in a center plate assembly between the car body center plate and the truck bolster bowl of a railroad car, wherein the liner includes a body having a self-lubricating load-bearing portion highly resistant to cold flow and at least one and preferably a plurality of compressible conductive resilient members resistant to cold flow and for providing electrical continuity between the truck bolster and the car body.
Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like numerals refer to like parts, elements, components, steps and processes.